If you are planning a rafting trip on the Colorado River, through Grand Canyon National Park, you will find that special permits are available through a weighted lottery. This allows you to experience a non-commercial river rafting adventure with your own private group.
These private river trips are the perfect way to go. Every month a certain number of trips are available. You can get all the details on the Weighted Lottery website. There are information pages where you can find out the available dates and which dates have been already filled. You should register on the site even if you will go later than 2008 or if all trips for 2008 are booked.
The application fee is $25, covering the main lottery and all follow-ups. When you win via the lottery, you are charged $400 deposit that goes toward the final $100 per person cost of the permit.